Optical polarization

About: Optical polarization is a research topic. Over the lifetime, 13992 publications have been published within this topic receiving 244284 citations.

Observed Polarization of Brown Dwarfs Suggests Low Surface Gravity

Abstract: Light scattering by atmospheric dust particles is responsible for the polarization observed in some L dwarfs. Whether this polarization arises from an inhomogeneous distribution of dust across the disk or an oblate shape induced by rotation remains unclear. Here, we argue that the latter case is plausible and, for many L dwarfs, the more likely one. Furthermore, evolutionary models of mature field L dwarfs predict surface gravities ranging from about 200 to 2500 m s{sup -2} (corresponding to masses of {approx}15-70 M {sub Jupiter}). Yet comparison of observed spectra to available synthetic spectra often does not permit more precise determination of the surface gravity of individual field L dwarfs, leading to important uncertainties in their properties. Since rotationally induced non-sphericity, which gives rise to non-zero disk-integrated polarization, is more pronounced at lower gravities, polarization is a promising low gravity indicator. Here, we combine a rigorous multiple scattering analysis with a self-consistent cloudy atmospheric model and observationally inferred rotational velocities and find that the observed optical polarization can be explained if the surface gravity of the polarized objects is about 300 m s{sup -2} or less, potentially providing a new method for constraining L dwarf masses.

Dual-Band LFM Signal Generation by Optical Frequency Quadrupling and Polarization Multiplexing

Abstract: A photonic approach to generating dual-band linear frequency modulation (LFM) signal is proposed based on optical frequency quadrupling and polarization multiplexing. This is achieved by using an integrated polarization multiplexing dual-parallel Mach-Zehnder modulator to perform frequency quadrupling in two orthogonal polarizations independently. After optical-to-electrical conversion, two LFM signals in different frequency bands can be generated simultaneously. The proposed scheme has a very simple and compact structure. Thanks to the frequency quadrupling technique, high-frequency, and wideband LFM signals can be generated with low speed electrical devices. The central frequency, bandwidth, and temporal duration of the generated LFM signals can be easily adjusted. In the experiment, the generation of dual-band LFM signals in K-band and Ka-band (centered at 20 and 30 GHz, respectively) is demonstrated. Tunability of the central frequency, bandwidth, and time duration is also verified. The proposed signal generator is a promising candidate in dual-band multi-function radar applications.

Nonlinear Decay Of High Order Optical Vortices In Anisotropic Optical Media

Abstract: Vortical excitations with quantized circulation appear in superfluids, superconductors, and nonlinear optics in the presence of a repulsive nonlinearity. The nonlinear Schrodinger equation (NLS) has been used extensively to describe vortex solitons in two transverse dimensions, as was done first in the context of vortex lines in superfluids by Ginzburg and Pitaevskii.1 Much recent attention has been attracted by vortices and vortex solitons in nonlinear optics.2 Kerr type optical media with a cubic, isotropic, and local nonlinearity have been shown experimentally to support stable (2 + 1)D vortex solitons.3

Submilliarcsecond Polarimetric Imaging of Blazar Jets at 43 GHz

Abstract: We present 43 GHz polarization images obtained with the Very Long Baseline Array of four blazars (0829+046, 1055+018, 1334-127, and AP Librae), as well as four active galactic nuclei, which served as polarization calibrators (DA 193, OJ 287, 3C 279, and 1611+343). Six of these objects are members of the Nartallo et al. millimeter-wave polarization blazar monitoring sample. We find no differences in the overall millimeter-wave polarization properties of the BL Lacertae objects and quasars in our sample. This is in contrast to previous findings at centimeter wavelengths, in which the inferred magnetic fields of quasars are found to be predominantly aligned with the jet, while perpendicular configurations are found in BL Lac objects. With the exception of 1611+343, a low optical polarization quasar, all of the unresolved blazar cores in our sample have inferred magnetic field orientations perpendicular to the inner jet direction. Past nonimaging millimeter-wave polarization monitoring data have shown that these core orientations are stable in three of our sample objects; this may be due to strong, unresolved standing shocks located very close to the base of the jet. We also detect in the jets of blazars a moderate-sized population of polarized components having electric vectors that lie at an oblique angle to the local jet direction. We find that the observed distribution of electric vector misalignment angles cannot be fitted by a single population of oblique shocks having arbitrary inclinations with respect to the jet axis. Such a population predicts an overabundance of shocks with electric polarization vectors aligned with the jet axis, produced by relativistic effects associated with the jet flow. We find the data to be more consistent with a scenario in which the polarized jet components are merely enhanced regions whose magnetic field orientations are controlled by some mechanism other than shocks.